Proposal Pending on Mileage for Heavy-Duty Vehicles

WASHINGTON — For three decades, the federal government has calculated the fuel economy of cars and other “light-duty vehicles” and periodically tightened mileage standards. For the first time, it is preparing to do the same with heavy-duty vehicles, which could greatly reduce their consumption of diesel fuel.

The Obama administration could announce a proposal as early as this week for new mileage standards for heavy-duty vehicles beginning in the 2014 model year. Separately, the administration is readying new fuel economy standards for light-duty vehicles in the 2017 model year and beyond, after tightening standards last year for 2012 through 2016 models.

The new standards would make it likely that technologies used in cars — aerodynamic bodies, low-rolling-resistance tires, variable valve timing and hybrid electric propulsion — would be introduced in box trucks, garbage trucks, cement mixers, school buses and tractor-trailers. But since heavy trucks are so varied, each of the technologies would be useful only in some types of vehicles.

The potential for improved fuel economy is considerable: a study issued in May by the National Academy of Sciences projected that fuel consumption in heavy-duty vehicles could be cut by one-third to one-half. Some of the technologies would make economic sense even at diesel prices of $1.10 a gallon, about a third of the current price, the study said.

Dr. Assanis, a professor at the University of Michigan who is director of its energy institute and automotive laboratory, said that while cars had become more efficient in the last few decades, holding down gasoline consumption, diesel use had risen.

The Obama administration is eager to see changes in the heavy-vehicle category because diesel fuel, used by most such vehicles, accounts for more than 10 percent of the nation’s oil consumption and about 20 percent of the greenhouse gases emitted by the transportation sector. (Diesel emits more greenhouse gases per gallon than gasoline.)

But the science academy study found that while the basic notion of miles traveled per gallon worked well for light-duty vehicles, the world of heavy-duty vehicles was “much more complicated.” As a yardstick for determining whether a fuel economy improvement is worthwhile for a heavy truck, it can be very misleading, the researchers said.

Some tractor-trailer trucks, for example, cover 100,000 miles a year, meaning that a small change in fuel economy can result in significant savings. But other vehicles — a fire engine, say, or a bucket truck used by electric companies to maintain overhead wires — travel very few miles.

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What is more, the bulk of a bucket truck’s fuel consumption is expended operating the bucket while the truck is stationary, making miles per gallon less of a consideration.

But Drew Kodjak, executive director of the International Council on Clean Transportation, said varied usage patterns should not slow the introduction of new rules. “There are really three classes of medium- and heavy-duty vehicles that matter: the tractor-trailer trucks, the large urban delivery trucks and the one-ton pickup trucks,” he said.

Those three categories account for 90 percent of fuel consumption and carbon dioxide emissions of vehicles to be covered by the rules, he said.

Fleet-truck buyers pay far more attention to fuel economy than car buyers. Nonetheless, “a lot of guys out there will go for the cheapest cab they can buy, the cheapest tires and the cheapest everything,” said David F. Merrion, an automotive engineer and a member of the science academy panel.

Regulation poses challenges because trucks do not have manufacturers in the same sense that cars do. Auto companies design engines, transmissions and bodies, assigning specifications for tires and other crucial parts made by other manufacturers. Heavy-duty vehicles, however, are very often assembled and sold by “integrators” that mix and match components.

“There is no Ford Motor Company in that value stream,” said Andrew Brown Jr., chief technology officer of the Delphi Corporation, who led the science academy study. “The players today generally don’t communicate with each other — they don’t have to.”

Another complication is that similar trucks may need vastly different equipment to comply with fuel standards. A hybrid electric system, for example, would be beneficial in stop-and-go traffic or over rolling terrain, but it would add useless weight to a tractor-trailer that cruises at 65 m.p.h. on flat terrain.

Duke Drinkard, a retired vice president at Southeastern Freight Lines who also participated in the science academy study, said that maximizing fuel economy would mean equipping a full-size tractor-trailer differently depending on whether it was hauling its maximum weight or a cargo limited by volume.

While heavy trucks may travel just five or six miles on a gallon of fuel, on a per-ton basis that can be more efficient, said Allen Schaeffer, executive director of the Diesel Technology Forum, a trade group. If the regulations encouraged shippers to break up loads and place them on smaller trucks, fuel consumption would rise, he said.

A version of this article appears in print on September 30, 2010, on Page B2 of the New York edition with the headline: Proposal Pending on Mileage For Heavy-Duty Vehicles. Order Reprints|Today's Paper|Subscribe